Exploration of the Effects of Environmental Factors on the Parameters Needed for the Calculation of the Maximum Pit Size for Stainless Steels 304L and 316L

Once nuclear fuel has been used, it gets stored into stainless steel canisters that are exposed to dry storage conditions. Over time, these canisters are susceptible to corrosion. The maximum pit size model is being used as an input to determine the location-specific risk to failure during the service life of these canisters. In order to estimate the largest pit size possible, important parameters are needed, such as the corrosion potential, repassivation potential, pit stability, and the conductivity of the electrolyte.

In this work, OLI Studio: Corrosion AnalyzerTM was used to calculate parameters for a variety of single salt solutions for stainless steels 304L and 316L. OLI was used to study salt solutions based on different degrees of saturation of stoichiometric dissolution of the alloys to better understand the process that occurs inside the active pits. Evans diagrams were extracted for those conditions to further understand the extent to which reactions control the outcome.

In conclusion, it was computationally determined that compounds that have equivalent chloride concentrations will produce the same or similar result. It was found that when the surface solution chemistry changes, the corrosion morphology does as well. At critical, higher temperatures, sharp transitions in the corrosion potential for stainless steel 304L will occur and will result in the corrosion potential being lower than the repassivation potential. Therefore, when the canister reaches a high enough temperature, it will change the corrosion attack from pitting to active, uniform corrosion. When comparing the two databases, it shows that the model used for stainless steel 304L and the inputs for the maximum pit size predictions are sensitive to the parameters used.